Formation and Oxidation of Nanosized Metal Particles by Electrochemical Reaction of Li and Na with NiCo2O4: X-ray Absorption Spectroscopic Study

详细信息    查看全文

• 作者：Alan V. Chadwick ; Shelley L. P. Savin ; Steven Fiddy ; Ricardo Alcá ; ntara ; Diego Ferná ; ndez Lisbona ; Pedro Lavela ; Gregorio F. Ortiz ; Jos&eacute ; L. Tirado
• 刊名：Journal of Physical Chemistry C
• 出版年：2007
• 出版时间：March 29, 2007
• 年：2007
• 卷：111
• 期：12
• 页码：4636 - 4642
• 全文大小：260K
• 年卷期：v.111,no.12(March 29, 2007)
• ISSN：1932-7455

文摘

X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS)spectroscopy have been used to investigate the electrochemical reactions of NiCo₂O₄ in lithium and sodiumtest cells. Nanosized particles of NiCo₂O₄ were prepared by the thermal decomposition of a mixed oxalateprecursor and used as active electrode material. Ni K and Co K XANES results give evidence of the successivesteps in the reduction mechanism of the oxide during the first cell discharge. In a first step NiCo₂O₄ reactswith lithium and sodium and the reduction of both Ni³⁺ and Co³⁺ to the 2+ oxidation state is shown by apeak shift to lower energy values. As a result, sodium oxide or lithium oxide and the transition metal monoxidesare formed. Second, metallic products are formed, in which the average coordination numbers of the nearestneighbors for Ni and Co derived from the EXAFS data are 4 and 5, respectively, associated with ca. 1 nmparticle size. These novel ultrafine particles are stabilized in the Li₂O matrix of the discharged electrodes.Reoxidation of the metallic products up to a divalent state of Ni and Co in the form of monoxides is achievedduring the charge process of the electrochemical cells.